This invention relates to a tool bit which will fit in a quick release chuck. A quick release chuck is used to quickly change tool bits in the chuck of a tool. A example of one such quick release chuck apparatus is described in U.S. Pat. No. 4,900,202 (incorporated by reference in its entirety herein), which discloses a spring biased sleeve disposed on a spindle for aligning one or more detent balls relative to a tool bit.
Tool bits are used for drilling and for driving fastener devices such as screws, nuts and bolts, and other work elements requiring rotational motion. The American National Standards Institute has a specification, known as ANSI B 107.4-1982, which pertains to the driving and spindle ends for portable powered and hand held machines using the tool bits. The standard reflects the long term and pervasive use of such tool bits and the large inventory of tools available.
Tool bits manufactured in accordance with the ANSI standard have a hexagonally shaped tail (in lateral cross-section) with a circumferential arcuate groove formed into the tail. A detent ball in a quick release chuck applies normal and tangential forces against the groove in the shank of the tool bit to hold the tool bit in place. This groove must be precisely machined in order for the ball to fit and lock the bit into the tool.
The tool bit is made up of two main parts. The first part of the tool bit is an elongated shank, which includes a working end and a tail end. The working end is the drilling head or driving head, according to the use of the tool. The second part of the tool bit is the hexagonally configured end which is mounted into the chuck of the tool. This later portion of the tool bit is known as the bit tail. Bit tails are made of precision machined metal hex stock. The circumferential groove is machined into the metal hex stock, and the metal hex stock is bored to receive the elongated shank of the tool bit, usually by friction fit. Each bit tail, therefore, must be machined to fit the end of the elongated shank onto the bit, in such a manner as to provide a tight friction fit between the bit tail and the elongated shank. It is known to mold zinc about a tail bit, with a hex-shaped outer surface. Using zinc molded over the shank, however, subjects the elongated shank to high temperatures, since the zinc must be molten as it is formed about the shank. The shank often deforms when subjected to the high temperatures, causing shrinkage and dimensional variations to the shank itself. Additionally, special equipment is typically needed to mold the zinc about the shank which can become cost prohibitive. The resulting shanks are heavy, adding to the cost of shipping the zinc molded shanks.
The invention is a tool bit that is used in a quick release socket or chuck mechanism. The tool bit has an elongated shank with on operative tip end and an opposite tail end. A polymer jacket is molded to extend along a portion of the tail end of the shank, and the jacket has a hex-shaped outer surface in lateral cross-section.
The invention is also characterized as a method for fastening a polymer jacket onto a metal tool bit. The method includes forming a portion of a tail end of the tool bit to be non-circular in lateral cross-section. The method further includes molding a polymer composition about the tail end of the tool bit, including at least the non-circular portion thereof, to define a polymer jacket which has, in lateral cross-section, a hex-shaped outer surface.